Blind or partially sighted people usually use a mobility or long cane for orientation, with which objects in a distance up to 1.2 m can be detected. The orientation with such a long cane has several disadvantages. Especially the distance to the detectable objects is very short.
A number of devices for blind or partially sighted people is known which use contactless distance measurement systems to rectify the disadvantages of the long cane. Different versions of such a contactless distance measurement system are known. These devices comprise a transmitter which sends out a measurement beam and if the beam is reflected by an object a receiver detects the reflected beam. The distance between the device and the object is determined either via a time of flight measurement or by triangulation. The measurement beam can be electromagnetic (IR-radiation or laser beam) or sonic. The determined distance will be converted into a distance-dependent correcting variable which will be supplied to an indicator that displays the distance in a way that is adapted to the needs of the blind and partially sighted persons. Such indicators use either acoustic or vibronic signals.
The DE-A1-37 43 696 reveals a mobility aid that use a contactless distance measurement system. A transmitter sends out an IR-beam or a laser beam. If the beam is reflected by an obstacle a receiver detects the reflected beam and an acoustic signal will be generated. Transmitter and receiver are put in a device that is carried in front of the blind persons body. The measured distance to the obstacle is indicated by the pitch and the volume of the acoustic signal.
The DE-A1-35 44 047 describes a mobility aid that works with a contactless distance measurement system which measure the distance to an obstacle by a so called sonic echo pulse time of flight method. A miniaturized sonic echo pulse time of flight evaluation device is put on the long cane. The pulses which are reflected by an obstacle are detected by a receiver and analyzed. The measured distance is converted into an acoustic noticeable audio frequency. This results in a kind of musical sequence of sounds if the distance to the obstacle decreases.
By the DE-A1-44 02 764 an other mobility aid using a contactless distance measurement system is known. In one housing comprises a radar signal transmitter, a radar receiver and a unit to analyze which produces a control signal if there is a frequency difference between the send and the received signals reflected by the surrounding. The control signal is supplied to a signal generator who is built as a kind of tappet pestle that is moving electromagnetic. The mechanic effect occurs on the body of the person through the force of pressure depending on the control signal. The radar system and the tappet pestle are arranged in a headgear. Within a further development of the mobility aid a second radar system and a second tappet is provided. The second radar system is arranged in a belt.
By the DE-A1-25 11 935 a further mobility aid for partially sighted persons using a contactless distance measurement system is known. Here the measured distance (or any measured value) is indicated acoustically by variation of the pitch and volume or vibronic through the variation of the vibrational frequency, the force of vibration and the kind of vibration.
Through the DE-A1-195 22 601 a further mobility aid for partially sighted persons using a contactless distance measurement system is known. A primary unit of the device comprises a sonic transmitter and a sonic receiver. A second unit comprises a micro computer for the receiver signals and a electro-mechanic vibrator as indicator.
Further devices using contactless distance measurement as orientation aid for blind and partially sighted people which use similar acoustic or vibronic indications are described in DE-A1-41 40 976, DE-A1-29 32 659, DE-PS-23 30 940, DE-A1-28 16 530, DE-A1-31 33 645, DE-A1-195 05 402, DE-A1-40 438 and DE-A1-38 36 961.
It turned out that the display of the indication devices of the known mobility aids for blind people working with contactless distance measurements is not satisfying. The main reason therefore is the difficulty of interpretation of those acoustic or vibronic signals. The assignment of a acoustic or vibronic signal to a determined distance needs a lot of practice. While the user receives the actually measured signal there is no reference signal (e.g. distance zero) to compare with. Furthermore, acoustic signals bother blind persons because they use their hearing for orientation in and perception of the environment.